It is known to include a plurality of integrated circuits in a single package body as a way to increase the density of integrated circuits on a printed circuit board. U.S. Pat. No. 5,815,372 Japan Patent 56062351 provide examples of packages having two integrated circuits.
Another method to increase package density is to mount a first small outline integrated circuit package (xe2x80x9cSOICxe2x80x9d) having either gull wing or J lead styles on a printed circuit board. Next, the leads of a second SOIC package are cut so as to form lead stubs. The second SOIC package is then stacked on the first SOIC package, and the lead stubs are soldered to the leads of the first SOIC package. Unfortunately, this method is difficult and time consuming. Moreover, the footprint of the first SOIC package is relatively large due to the gull wing or J-style leads. Japan Patent 56062351 shows a stack of two packages.
U.S. Pat. No. 5,835,988 discloses packages that can be stacked in multiple layers.
The present invention provides packages that may easily be stacked one on top of another. Stacking the packages allows an increase in the density of packages on a printed circuit board without a corresponding increase in the area of the printed circuit board consumed thereby. Moreover, there are many ways of stacking and/or inter-connecting the packages, which gives the user great flexibility. In addition, the packages may be stacked and mounted on a printed circuit board without soldering the packages to each other or to the printed circuit board.
One embodiment of a stackable package within the present invention includes a molded package body having a bottom first surface, an opposite top second surface, side surfaces extending vertically between the first and second surfaces, and one or more stacking clips. The stacking clips are integrally connected to a side of the package body. Each stacking clip is adapted to engage a package body of a similar stackable package that is to be stacked with the package having the clip. An electronic device, such as an integrated circuit chip or a micro-machine, is within the body of the stackable package.
In one exemplary embodiment, the clip has the form of a cantilever beam, and includes a free end distal from the package body. A recess is formed in an upper, outer portion of the clip adjacent to the connection between the clip and the respective package side. The free portion of the clip has a protuberance at its distal end. The protuberance is formed so as to fit within the recess of a similar package stacked with the package having the clip.
The stackable package also includes a plurality of leads that are each electrically connected to the electronic device. Each lead has a first portion embedded at a bottom surface of the package body and having a first surface exposed at the first surface of the package body, a second portion that extends vertically adjacent to a side surface of the package body, and a third portion that extends over the top surface of the package body.
In one embodiment, the leads are formed of a spring metal, such as spring copper, and have a spring member, such as a crook shaped spring, formed into the lead. The spring metal and spring member cause the lead to apply a continuous force against the leads of another package stacked upon the package having these features, thus providing a solderless electrical connection between the stacked packages and securing the stacked packages to each other.
The stacking clips, spring metal leads, and spring member, or some combination thereof, can be incorporated into the various packages described below to ensure a secure, solderless electrical connection between the stacked packages. The stacking clips also can be engaged with a printed circuit board so that one package or a module of stacked packages can be securely mounted on a substrate, such as a printed circuit board, so that the leads of the package are electrically connected thereto.